This is a request for a five year renewal of an NIH grant focusing on hemispheric specialization and interaction at the interface of language and cognition. A convergent research program is outlined which studies neurological patients and normal subjects and combines behavioral and anatomical methods. Technological developments include a powerful computer-based laboratory for laterality research and an eye-tracker with scotoma simulator for hemispheric ocular scanning without attachments to the eye. Theoretical work will continue on behavioral models of laterality effects and conditions for parallel independent processing in the two hemispheres. One set of experiments will study independent lexical access and organization, syntactic and pragmatic competence and associated cognitive abilities in each of the two hemispheres, including the ability to learn new linguistic material and to monitor and correct errors. In parallel, other experiments will study hemispheric independence in processing and monitoring nonverbal tasks, including visual imagery, visual illusions, face recognition, and object classification. Another set of experiments will analyze individual differences in regional patterns of callosal connectivity using behavioral and anatomical measures, especially in relation to cognitive profile. Biological and environmental conditions that change callosal connectivity will be investigated. Neuropathological sections of the callosum will be compared to MRI measures, and used to count fibers of different types in several regions. Results promise better understanding and possible control of cognitive pathology due to abnormal cerebral activation or faulty interhemispheric communication. The data will contribute to theoretical cognitive neuroscience by understanding how language is organized in the brain and how independent, parallel cortical processing modules interact.